Treatment of residual liquors



Patented Aug. 2, 1927.

\ UNITED STA TES- \LINN BRADLEY, or uon'ronam, NEW JERSEY, m: EDWARD, 2. measure, or new YORK, N. N. Y., A CORPORATION OF NEW YORK.

'Y., ASSIGNORS TO BRADLEY-McKEEFE CORPORATION, OF NEW YORK,

. TREATMENT OF RESIDUAL L IQ'UOBS.

No Drawing. Application filed February 7,- 1922, Serial No. 534,768. Renewed October 15, 1 928.

This invention relates to the-treatmentof the residual liquors from the product-ion of wood pulp with a cooking liquor containing sodium monosulfite, or a mixture of sodium or sulfate process,

monosulfite and caustic soda.

In certain companion applications we have described a new and'useful method of producing wood pulp from wood by subjecting the wood to a cooking operation, under pressure and at an elevated temperature,,with a cooking liquor consisting essentially of sodium .rnonosulfite, or sodium monosulfite together with a limited amount of caustic soda. Such processes result in the production of increased yields ofa superior and improved pulp, containing fibers of great strength, which have not been objectionably injure by the cooking operation.

The present in ment of the residual liquors from such processes, whereby the processes may be made regenerative or cycllc in character.

The residual liquors produced by such pulp processes .are of distinctive and characteristic composition. They contain a decreased content of organic matter, as compared with the black liquor. from the soda due to the fact that incrusting and non-fibrous constituents are dissolved or removed from the wood without dissolving or removing any considerable amount of the fibers themselves, whereas,

in the soda and sulfate processes, a considerable amount of the fibers is dissolved and goes into the residual liquor.

The composition of the residual liquors which are treated according to the present invention will vary somewhat with difl'erent woods, and with the particular composition of the cooking liquor. With deciduous woods, such as poplar, bass wood, -maple, birch, beech, oak, etc.,, and with certain coniferous woods, such as spruce, pines, etc. the cooking operation may be carried out with a cooking liquor containing essentially normal sodium sulfite. With other woods, particularly highly resinous woods, such as certain pines, the cooking liquor may contain .a sufficient amount of caustic soda, in addition to a preponderating proportion of sodium sulfite, so that the resinous and other ention relates to the treat- I -stituents, the liquor frequently contains so dium carbonate and some sodium acetate,

sodium formats, sodium oxalate, sodium ,resinates and some sodium sulpho-organic compounds. The liquor may contain soaps or materials of a similar character resulting from the combination of the sodium sulphite or caustic soda or both with saponifiable constituents of the wood treated, particularly in the case of resinous woods Where resin soaps or compounds of a similar character may be formed in considerable amounts.

It may also contain tanning material, dyes and other dissolved organic material.

'The residual liquor is mahogany in color, but the color varies somewhat in intensity with different Woods and is somewhat darker when small amounts of caustic are used. In reaction the liquor is alkaline to litmus but not strongly alkaline'unless caustic has been employed, the degree of alkalinity obviously depending upon the amount of caustic' used.

In consistency the residual liquor may be thinner than black liquors commonly obtained by soda? and sulphate processes, and

it may contain, a smaller proportion of solids in solution because the cellulose is not attacked and dissolved by sodium sulphite to any great extent during the pulp-making operation.

One purpose of the present invention is. the recovery of' aluable constituents of the residual liquor, particularly the sulphite radical and sodium content, so that these are consequently made available for the treatment of further quantities of wood. Incidentally,other valuable and useful products are recovered or made available.

Where a considerable excess of sodium sulphite is employed in the @oking liquor, the residual liquor may still contain considerable ofthis material in a free state, and merely by concentrating the residual liquor some of the unconsumed sodium sulphite can be crystallized out upon the cooling. When the liquor is concentrated directly in this way, exposure to the air during concentration should be avoided as much as possible in order to prevent conversion of the sulphite into sulphate. This concentration may be employed as the preliminary step in the treatment of the residual liquor, the recovered sodium sulphite being immediately available for reuse whilaother valuable materials in the residual liquor are recovered by further treatment.

As a further preliminary step, a portion of the dissolved organic matter may in some cases be separated by treating the residual liquor with suitable acids, rendering it acid in reaction. The precipitated organic matter can then be filtered ofi', leaving a clear liquor containing a decreased content of dissolved organic matter and being thus more readily susceptible to further treatment for the recovery of the sulphite radical and sodium ion remaining therein. The precipitated organic matter, as it is separated from the solution, is light in color and may be advantageously used for a variety of purposes, for example, as a sizing material, as an ingredient for plastic compositions, etc.

For the further treatment of the residual liquor or for the 'treatment of such liquor without preliminary treatment as hereinbefore set forth, the addition of sulphur dioxide in quantities suflicient to convert sodium compounds into sodium sulphite at fords an efi'ective method of recovering sodium sulphite for reuse as a cookingliquor. Following the treatment with sulphur dioxide, some organic matter present in the solution maybe separated and the liquor is then ready for further use after theaddition of suflicient sodium sulphite to make up the material consumed in the cooking operation. A portion of the sodium sulphite may be causticized by the addition of calcium hystallizes out on cooling, Further concentradroxide if the presence ofcaustic soda in the liquor is desirable. 7

Where considerable caustic soda has been employed'in combination with the sodium sulphite, as in the treatment of certain woods, sulphur dioxide may be added, (together with sodium bisulphite, the latter being added in amount sufiicient to make up the loss of soda), to combine with any unused causic soda and .to displace some of the'organic-acid radicals, thus increasing the yield of sodium sulphite. If the organic radical released is insoluble in the neutral or acid liquor, as for example, the resins, gums, etc., a cbnsiderable amount of sodium sulphite may be recovered from sodium organic compounds present in the liquor. Thus the residual liquor from the cooking of resinous woods, such as spruce (and especially pines) contains sodium organic compounds which may be converted into sodium sulphite by treatment with sulfur dioxide. Following the treatment described, the liquor may be clarified and causticized to the desired degree by the addition of calcium hydroxide. Any calcium sulphite resulting while neutral or alkaline with gypsum (calcium sulphate) which will react with the sodium sulphite and precipitate calcium sulphite, leaving sodium sulphate in solution. In this manner, substantially all of the sulphite radical existing as sodium sulphite can 'be precipitated vfrom the liquor. Preferably a slight excess of gypsum is employed to insure complete precipitation. This precipitation may be carried out either before or after concentration of the residual liquor and the solution containing the sodium sulphate may be concentrated to a greater or less degree. So long as the solution is slightly alkaline or neutral, the calcium sulphite will be precipitated without any appreciable occlusion of organic matter, and the organic matter will thus remain in solution with sodium sulphate. The precipitated calcium sulphite may be removed from the liquor by filtration, decantation, sedimentation or otherwise. Thus it may be permitted advantageously to settle so that the liquor may be drawn off, leaving the calcium sulphite for further use as hereinafter described.

The solution containing the sodium sulphate and organic/matter may be concentrated by evaporation or otherwise until the greater portion of the sodium sulphate cryswashing of the pulp, and added to the calci- 'um sulphite precipitate produced as above described. If an acid such as sulphuric acid or nitre cake (acid sodium sulphate) or an excess of sulphur dioxide is then added, the calcium sulphite will react with the sodium sulphate, precipitating gypsum and leaving sodium sulphite in solution. The use .or

Ill)

nitre cake as an acidifying agent is desirable inasmuch as the sodium of the nitre cake is thus added to the liquor, making up any losses of sodium in the process. The acid solution may be neutralized with calcium hydroxide, thus producing a further precipitate of calcium sulphate. The calcium sulphate may be separated from the liquor by filtration, decantation, sedimentation or otherwise and utilized again in the treatment of further amounts of residual liquor.

The solution of sodium sulphite obtained as above, with proper regulation of its conseparated from the solution. The excess acid used for acidifying the liquor assists in bringing about the reaction of sodium sulphate and calcium sulphite, or a further amount of acid ma be added if necessary.

Itlwill be note that the process as described involves the treatment of the residual liquor with calcium sulphate while the liquor is neutral or alkaline with resulting reaction of the calcium sulphate and sodium sulphite to give a precipitate of calcium sulphite and a solution of sodium sulphate.

This sodium sulphate solution, after the separation of organic matter therefrom, is caused to react with the calcium sulphite in the presence of a sufficient amount of the acid to reproduce the sodium sulphite in solution with precipitation of calcium sulphate, The direction of the reaction thus depends uson .Whether the solution is alkaline or aci The calcium sulphate and calcium sulphite used as reagents are continu- )usly regenerated so that it is necessary only to add a suflicient amount of these materials from time to time to make up for losses. When lime is used for neutralizing the acidity, or nitrc cake or sodium bisulphate to give the. necessary acidity, they also serve to make up any loss'esof calcium and of sodium in the process.

In the treatment of sodium sulphate solution with calcium sulphite and sulphurous acid as above described, it is preferable to employ less sulphurous acid than the amount necessary for the production of sodium bisulphite as the. amount of sulphur dioxide as well as of calcium compounds required in the process is thus reduced to a minimum.

A considerable amount of high grade calciumsulphate is obtained in the process and some of it may be reused while the balance is available for use as a paper filler or for any other purpose to which it is adapted. We claim: 1. The method of treating residual liquor from the production of pulp with a cooking liquor containing essentially sodium sulfite or sodium sulfite and caustic alkali which comprises concentrating the residual liquor and crystallizing sodium sulfite therefrom. 2. The method of treating residual liquor from the production of pulp with a cooking liquor containing essentially sodium sulfite or sodium sulfite and caustic alkali which comprises acidifying the residual li uor and separating precipitated organic matter therefrom.

3. The method of treating residual liquor from the production of pulp with a cooking liquor containing essentiall sodium sulphite or sodium sulphite an caustic alkali, which comprises subjecting the residual liquor to the action of the sulphite radical to regenerate sodium sulphite.

4. The method of treating residual liquor from the production of pulp with a cooking liquor containing essentially sodium sulphite. or-sodium sulphite and caustic alkali, which comprises subjecting the residual'liquor to the action of the sulphiteradical to regenerate sodium sulphite and thereafter neutralizing the solution.

5. The method of treating residual liquor from the production of pulp with a cooking liquor containing essentially sodium sulphite or sodium sulphite and caustic alkali, which comprises subjecting the residual liquor to the action of the sulphite radical to regenerate sodium sulphite and causticizing a portion of the solution to rovide the desired proportion of caustic a ali therein.

6. The method of treating residual liquor from the production of pulpiwith a cooking liquor containing essentially sodium sulphite or sodium sulphite and caustic alkali, which comprises concentrating the residual liquors, crystallizing'sodium sulphite therefrom and then subjecting the liquor to the action of the sulphite radical to regenerate sodium sulphite.

7. The method of treating residual liquor from the production of pulp with a cooking liquor containing essentially sodium sulphite or sodium sulphite and caustic alkali, which comprises acidifyingthe residual liquor, separating precipitated organic matter therefrom, then subjecting the liquors to the action of the sulphite radical to regenerate sodium sulphite. v

8. The method of treating residual'liquor from the production of pulp with a cooking liquor containing essentially sodium sulphite or sodium sulphite and caustic alkali, which comprises subjecting the residual liquor to the action of sulphur dioxide to regenerate sodium sulphite.

9. The method of treating residual liquor from the production of pulp with a cooking liquor containing ementially sodium sulphite or sodium sulphite and caustic alkali, which comprises subjecting the residual liquor to the action of sulphur dioxide and sodium bisulphite to regenerate sodium sulphite.

10. The method of treating residual liquor from the production of pulp with a cooking liquor containing essentially sodium sulphite or sodium sulphite and caustic alkali, which comprises subjecting the residual liquor to the action of sulphur dioxide to regenerate sodium sulphite and separating precipitated organic matter from the liquor.

11. The method of treating residual liquor from the production of pulp with a cooking liquor containing essentially sodium sulphite or sodium sulphite and'caustic alkali, which comprises subjecting the residual liquor to the action of sulphur dioxide to regenerate sodium sulphite and causticizing a portion of the liquor to provide the desired proportion of caustic alkali therein.

12. The method of treating residual liquor from the production of pulp with a cooking liquor containing essentially sodium sulphite or sodium sulphite and caustic alkali, which comprises subjecting the residual liquor to the action of sulphur dioxide and sodium hisulphite to regenerate sodium sulphite and separating precipated organic matter from the liquor.

13. The method of treating residual liquor from the production of pulp with a cooking liquor containing essentially sodium sulphite or sodium sulphite and caustic alkali, which comprises subjecting the residual liquor to the action ofsulphur dioxide and sodium bisulphite to regenerate sodium sulphite, and causticizing a portion of the liquor to provide the desired proportion of caustic alkali therein.

14:. The method of treating residual liquor from the production of pulp with a cooking liquor containing essentially sodium sulphite or sodium sulphite and caustic alkali, which comprises causin the residual liquor, while neutral or alkaline, to react with calcium sulphate, with production of a precipitate of calcium sulphite and a solution containing sodium sulphate, separating the sodium sulphate from most or all of the organic matter and causing the sodium sulphate to react with precipitated calcium sulphite in the presence ofa sulficient amount of acid to form a precipitate of calcium sulphate and a solution of sodium sulphite.

15. The method of treating residual liquor phate and a solutionof sodium sulphite for reuse in the pulp-making process.

16. The method of treating-residual liquor from the production of pulp with a cooking liquor containing essentially sodium sulphite or sodium sulphite and caustic alkali, which comprises treatin the residual liquor while alkaline with ca cium sulphate to .give a' precipitate of calcium sulphite and a solution containing sodium sulphate, concentrating the resulting solution, acidifying to precipitate organic matter therefrom, separating the organic matter, causing the resulting solution of sodium sulfate to react with the precipitated calcium sulfite in the presence of a sufiicient acid to give a precipitate of calcium sulphate and a solution of sodium sulfite for reuse in the process.

17. The method of treating residual liquor from the production of pulp with a cooking liquor containing esscntially sodium sulphite or sodium sulphite and caustic alkali, which comprises treating the residual liquor, and while alkaline in reaction, with calcium sulphate-to give a precipitate of calcium sulphite and sodium sulphate in solution, evaporating the solution to dryness, burning the organic matter therein, redissolving the sodium sulphate and causing the solution to react with the precipitated calcium sulphite in the presence of a suficient amount of acid to give a precipitate of calcium sulphate and a solution of sodium sulphite.

18. The method of treating residual liquor from the production of pulp with a cooking liquor containinglessentially sodium sulphite or sodium sulphite and caustic alkali, which comprises treating the vresidual liquor with potassium sulphite to regenerate sodium sulphite and to form potassium compounds with organic acids in solution, concentrating the solution, crystallizing sodium sulphite therefrom and recovering the potassium organic compounds.

In testimony whereof we afix our signatures.

LTNN BRADLEY. EDWARD ll MOKEEFE. 

